OBJECTIVE OF THIS INVESTIGATION: With oral psoralen, ultraviolet A (PUVA) treatment rapidly becoming a widely used method of treating psoriasis and other diseases, it is important to determine as accurately as possible the morphologic effects of PUVA on both normal and psoriatic skin. This project will study: 1) effects on epidermal ultrastructure; and 2) ultrastructural changes in dernal tissue. Major goals of this study are consistent with those of the Oral Methoxysalen Photochemotherapy Trial, which are: 1) confirm the safety and effectiveness of oral psoralen photochemotherapy for psoriasis, and 2) closely follow the population of patients for possible long-term morphologic effects of therapy with the light and electron microscope. To be studied in 3 mm cutaneous punch biopsy specimens are: A. Epidermal ultrastructural changes: 1) keratinocytes and keratinization; 2) melanocytes and melanogenesis; 3) Langerhans cells; 4) lysosmes. B. Dermal connective tissue: 1) ultrastructural alterations in collagen and elastin in the dermis; 2) blood vessels and cells. C. Basal lamina.